1. Field of the Invention
The present invention relates to an image controller adapted to output an image of a mixture of pictorial plots, character plots and graphic plots through processing of the plots corresponding to each kind of plots.
2. Description of the Prior Art
In a conventional printer controller or the like, the image of a pictorial plot among a mixture of characters, graphics and pictorial plots has been converted to a pseudo halftone image through binarization according to the systematic dithering, and the image has been output as it has been stored in a binary image memory.
On the other hand, in order to enhance the image quality of a pictorial plot such as a photograph or the like, a multi-level image memory of three planes has been used to store the images of characters, graphics and pictorial plots, and the image data in the image memory has been output as it is to a printer. The image of the pictorial plot in this case is known to be a digital halftone image processed by the eight-level dither method (e.g., described in Vol. 1, No. 5, pp. 58-67 of "MACWORLD JAPAN").
In the above-described conventional technique, the images of different characteristics have been processed in the same fashion. In other words, although the images of the characters and graphics are binary, the images of the pictorial plots are represented in the multi-level halftone expression. Therefore, when an image of a mixture of these kinds of plots is stored by a binary image memory, the portion of the pictorial plots results in a harsh image and the quality of the total image is greatly worsened.
With much importance given to the pictorial plots, if a multi-level image memory constituted of three planes and capable of expressing in eight-level by one pixel is used to store the image of the mixed plots, the above drawback that the portion of the pictorial plots is harsh is improved, but the storage capacity is required to be increased.